Why Kubernetes Cluster Autoscaler Loses to Karpenter After 6 Months in Production

Most teams adopt Cluster Autoscaler (CA) because it ships with EKS and works on day one. Six months later , they're staring at 12 node groups nobody fully owns, a cost report showing 30% idle capacity during off-peak hours, and a backlog of scaling incidents that hit during the morning traffic ramp. The switch to Karpenter fixes those problems because the architectures are fundamentally different, not because Karpenter is a newer version of the same thing. This post covers what we've seen in pro